Typy mapowane: przekształcanie typów obiektów

type Copy<T> = { [K in keyof T]: T[K] };
type UserCopy = Copy<User>; // same as User

type Partial<T> = { [K in keyof T]?: T[K] };
type PartialUser = Partial<User>;

type Readonly<T> = { readonly [K in keyof T]: T[K] };
type FrozenUser = Readonly<User>;

type Stringify<T> = { [K in keyof T]: string };
type StringUser = Stringify<User>; // all values are string

type OnlyStrings<T> = {
  [K in keyof T as T[K] extends string ? K : never]: T[K]
};

type Record<K extends string | number | symbol, V> = { [P in K]: V };
const roles: Record<'admin' | 'user', boolean> = { admin: true, user: false };

interface User { id: number; name?: string; }
type Copy<T> = { [K in keyof T]: T[K] };
type C = Copy<User>; // id: number; name?: string (preserved)

type Getters<T> = {
  [K in keyof T as `get${Capitalize<string & K>}`]: () => T[K]
};

type Flags = { [K in 'option1' | 'option2' | 'option3']: boolean };

type NullableValues<T> = { [K in keyof T]: T[K] | null };